The present invention relates to a heat shrinkable polyester film. The present invention also relates to a heat shrinkable polyester tube obtained using the heat shrinkable polyester film, a production method thereof and to a container wearing this heat shrinkable polyester film. The heat shrinkable polyester film of the present invention has, in addition to suitable heat shrinkable properties, superior printing property, adhesion property by the action of a solvent, superior appearance when used for packaging such as covering, bundling and the like, and mountability. Furthermore, the heat shrinkable polyester film of the present invention has a small apparent specific gravity, and can be collected separately from a bottle after use relatively easily after fitted to the bottle (such as PET bottle) as a label.
A heat shrinkable tube made of a heat shrinkable plastic film is used as a covering or a bundle of, for example, containers such as bottles (e.g., plastic bottles etc.), cans and the like, rods (e.g., pipe, rod, wood etc.), plates, boxes and the like. Particularly, a heat shrinkable tube is widely used for a broad range of purposes, such as indication, protection, bundling, improved commercial value and the like of the contents of containers, by covering a part of the containers (e.g., cap, shoulder, body etc.) or the whole surface thereof, for packaging the containers, rods, plate-like products (e.g., notebooks etc.), boxes and the like by adhesion (e.g., collective packaging, skin-packaging etc.) and the like, and the development of use relying on shrinkability and shrinking stress is expected.
For the above-mentioned purposes, materials of heat shrinkable films, such as polyvinyl chloride, polystyrene, polyethylene, rubber hydrochloride and the like, are used, which film is processed to give a tube to cover the aforementioned article to be packaged and shrunk or, plural articles are collectively packaged with a tube-like film and the film is shrunk by heat. However, the heat shrinkable film made from these materials has defects in that it has poor heat resistance and cannot maintain a film state, because it is melted or burst easily by a boil treatment or retort treatment at a high temperature.
While a heat shrinkable film is often used after printing, when the above-mentioned heat shrinkable film is printed, printing pinholes are produced due to defective transfer of ink, because fine irregularities are produced by the additives and gelled polymer in the film (fish eye). Even when printing proceeded successfully, there remains a problem in that the film shrinks (shrinkage at normal temperature) after printing, thus resulting in a different printing pitch.
In recent years, a heat shrinkable polyester film has been drawing much attention claiming that the above-mentioned defects in conventional heat shrinkable films can be dramatically improved.
However, the conventional heat shrinkable polyester film is associated with a problem in that it has a greater heat shrinkage rate than a heat shrinkable film made from the aforementioned polyvinyl chloride, polystyrene, polyethylene, rubber hydrochloride and the like. A greater heat shrinkage rate causes shrinkage spots in a film that markedly reduce the commercial value. For example, when a conventional heat shrinkable polyester film is used to produce a shrink label for bottles, the great shrinkage rate causes concentration of shrinkage spots on a bottle shoulder, where the shrinkage rate becomes the highest, inclusion of air bubbles in the seal part, that failed to escape smoothly from the inside, and other problems. These problems in the heat shrinkable polyester films in turn cause inconsistent density of print, degrade the appearance of the resulting products, and therefore, remain to be solved.
Moreover, heat shrinkable polyester films are frequently used as labels of plastic bottles, particularly PET bottle and the like. For a recycled use of the PET bottle, attached labels need to be separated from the PET bottle. One of the separation methods comprises pulverizing the PET bottle with the attached label, stirring the pulverized product as it is or in water, and separating the label from the starting material of the PET bottle based on different specific gravities. When this method is employed, since PET, which is the main starting material of the bottle, has a specific gravity of about 1.4, the specific gravity of the label needs to be adjusted to below 1.4. However, the specific gravity of conventional polyester for labels cannot be decreased with ease.
To solve the above-mentioned problems, an attempt was made to add a thermoplastic resin incompatible with polyester, such as polyolefin polymer, polystyrene and the like, to the polyester to achieve a suitable heat shrinkage rate, or stretch the resulting material according a certain method to form voids in the polyester film, thereby to lower the apparent specific gravity after shrinkage. Such porous polyester film can be obtained according to the method described in, for example, JP-B-33063/1995, JP-A-111960/1993 and the like. Still, the aforesaid porous polyester films have the following problems.
(1) Due to insufficient brightness, the printing property is poor and due to the too high a total light transmittance, the content of the container can be seen through and the appearance of a label and a product is impaired upon actual use of the film as the label on the product.
(2) When voids in the film are increased to enhance brightness and decrease the total light transmittance, a number of voids are formed on the film surface as well, which in turn makes the surface roughness too high, printing property defective and appearance of the label poor.
(3) Because of the higher surface roughness, the surfaces of the splicing areas cannot be adhered to each other by the use of a solvent when processing a heat shrinkable film into a tube. Consequently, an adhesive and the like is required for the adhesion of the surfaces of the splicing areas, making the processing complicated. This method also makes the splicing areas easily damaged. As a result, the splicing areas do not permit superior heat shrinkage but cause whitening and embrittlement, and the appearance of a label becomes poor.
(4) The surface roughness of the print-and that of other surfaces are not balanced well, and the mountability and good appearance of product cannot be achieved at the same time.
(5) Because the apparent specific gravity is too high, separation and recovery based on different specific gravities after use as a label on a PET bottle etc. is difficult.
Therefore, there is a need for a heat shrinkable polyester film having suitable heat shrink property, superior printing property, permitting adhesion with a solvent, and superior appearance and mountability when used for packaging. In addition, a smaller apparent specific gravity of the polyester film is desired to be achieved.
According to the present invention, the following heat shrinkable polyester film is provided, which is superior in printing property, permits adhesion with a solvent, is superior in appearance and mountability, and which has a small apparent specific gravity.
The present invention provides the following:
(1) a heat shrinkable polyester film having a brightness of not less than 70, which permits adhesion with a solvent,
(2) the heat shrinkable polyester film of the above-mentioned (1), comprising voids,
(3) the heat shrinkable polyester film of the above-mentioned (2), wherein the voids are formed by forming a polyester comprising an incompatible thermoplastic resin into a film and stretching the film at least uniaxially,
(4) the heat shrinkable polyester film of the above-mentioned (2), comprising a polyester layer having many fine voids (layer A) and a polyester layer (layer B) having a smaller porosity than layer A, which is formed at least on one surface of the layer A,
(5) the heat shrinkable polyester film of the above-mentioned (4), wherein the layer A is a porous polyester layer having a porosity of 5-50 vol %, and the layer E is a porous polyester layer having a porosity of 0-20 vol %,
(6) the heat shrinkable polyester film of the above-mentioned (5), which further comprises a polyester layer (layer C) having a porosity of 0-50 vol % formed on the other side of the layer A where the layer B is not formed,
(7) the heat shrinkable polyester film of the above-mentioned (1), which has a center line mean surface roughness of at least one surface of not more than 0.5 xcexcm,
(8) the heat shrinkable polyester film of the above-mentioned (7), which has a total light transmittance of not more than 30%, and a percentage of heat shrinkage in hot air at 95xc2x0 C. of 30-90% in either direction of the heat shrinkable polyester film,
(9) the heat shrinkable polyester film of the above-mentioned (8), wherein the film has a heat shrinkage percentage of 0-10% in a direction perpendicular to said direction,
(10) the heat shrinkable polyester film of the above-mentioned (7), wherein the center line mean surface roughness (Ra1) of one surface is not more than 0.5 xcexcm and the center line mean surface roughness (Ra2) of the opposite surface is greater than Ra1 by not less than 0.05 xcexcm,
(11) the heat shrinkable polyester film of the above-mentioned (1), which further comprises organic or inorganic fine particles having a mean particle size of 0.001-5.0 xcexcm as a lubricant in a proportion of 0.01-30 wt %,
(12) the heat shrinkable polyester film of the above-mentioned (4), wherein the layer A comprises organic or inorganic fine particles having a mean particle size of 0.001-5.0 xcexcm as a lubricant in a proportion of 0.01-30 wt %,
(13) the heat shrinkable polyester film of the above-mentioned (1), which has an apparent specific gravity of less than 1.1,
(14) the heat shrinkable polyester film of the above-mentioned (1), which has an apparent specific gravity of less than 1.1 after heat shrinkage in at least one direction by 5-50%,
(15) the heat shrinkable polyester film of the above-mentioned (1), which further comprises at least one residue selected from a neopentylglycol residue and a cyclohexanedimethanol residue as a component of the polyester,
(16) the heat shrinkable polyester film of the above-mentioned (1), which has a film thickness of 10-100 xcexcm,
(17) the heat shrinkable polyester film of the above-mentioned (4), wherein the layer A has a thickness ratio to the layer B of 1.5-30,
(18) the heat shrinkable polyester film of the above-mentioned (1), which comprises a print on at least one surface,
(19) a heat shrinkable polyester tube obtained by adhering the heat shrinkable polyester film of the above-mentioned (1) with a solvent,
(20) a container equipped with the heat shrinkable polyester film of the above-mentioned (1), and
(21) a method for producing a heat shrinkable polyester tube, which method comprises the steps of applying at least one solvent selected from solvents having a solubility parameter within the range of 8.0-13.8 to at least one splicing area of the heat shrinkable polyester film of the above-mentioned (1); splicing the heat shrinkable polyester film at splicing areas at a temperature of not more than 70xc2x0 C.; and drying the spliced film to give the tube.